Damage to larynx can occur due to the following types of injuries:
1. Penetrating injuries
2. Blunt trauma - High / low velocity injuries.
3. Gun shot wounds
With the advent of compulsory seat belt regulations and improvement in vehicle safety measures has reduced the incidence of laryngeal trauma in car drivers. It is still more prevalent in two wheeler drivers. It is more common in females because of their thin long necks.
This is in fact a surgical emergency because of its life threatening effects on airway. In addition to impending threat to airway, these patients may also have the risk of associated injuries like cervical spine fracture, intra cranial injuries, and oesophageal injuries.
Trauma to larynx can be classified in two ways:
1. Classification according to the region of larynx involved (i.e. anatomical classification) - Supra glottic, Glottic and subglottic types.
2. Classification according to the type of tissue involved (i.e. skeleton / soft tissue).
Classification really plays an important role in deciding the management modality.
Features of supraglottic injury:
1. Horizontal fracture of thyroid ala
2. Disruption of hyoepiglottic ligament
3. Superior / posterior displacement of epiglottis
4. False lumen infront of epiglottis causing cervical emphysema
5. Hyoid bone fractures occur in the central portion of hyoid bone because the cornua are stronger. These fractures are common in women.
Features of Glottic injuries:
Trauma in this region causes cruciate fracture of thyroid cartilage at the point of attachment of vocal folds. These patients have sudden aphonia following injury.
Features of subglottic injuries:
Injury to cricoid cartilage causes injury to cricothyroid joint. Bilateral recurrent laryngeal nerve palsy can occur in these patients compromising the airway.
Injury to inferior cornua of thyroid cartilage may cause cricothryoid muscle dysfunction. These patients loose their ability to control the pitch of their voice.
1. Hoarseness of voice
2. Laryngeal tenderness
3. Cervical emphysema
6. Ecchymosis over neck
7. Loss of anatomical land marks
8. Presence of bony crepitus in the neck
Depending on clinical features these injuries are classified under four groups. This classification helps in deciding the optimal management modality.
Group I: These patients manifest with minor airway symptoms. Clinically these patients have minor hematomas, lacerations without clinical evidence of fracture larynx. These patients are kept under observation with head elevation. These patients are oxygenated using humidified air.
Group II: Patients in this group have airway compromise. These patients show evidence of edema / hematoma. These patients show minor exposure of mucosa. There is no evidence of cartilage exposure. Attention should be paid to secure the airway of these patients. Tracheostomy may have to be resorted to. Direct laryngoscopy and oesophagoscopy is performed to access the degree of injury.
Group III: Patients in this group have airway compromise. The degree of edema and hematoma is severe. Mucosal tears are extensive with evidence of cartilage exposure. Vocal cords are immobile in these patients. These patients need tracheostomy to secure airway, direct laryngoscopy and oesophagoscopy to assess the extent of damage. Exploration and repair of the wound should be resorted to. These patients dont need stents.
Group IV: Patients in this group have airway compromise. There is severe edema and hematoma. These patients have severe mucosal tears with cartilage exposure. Vocal cords are immobile. Tracheostomy is resorted to in these patients to secure airway. Exploration and repair of the wound is necessary. Stenting should also be done to prevent stricture to airway.
CT scan is the preferred modality of investigation. It helps to identify occult damage to larynx. Ofcourse it plays very little role in determining the optimal management modality.
Since MRI scanning time is rather prolonged, it is not a popular imaging modality in this condition which is a surgical emergency.
Biomechanics of laryngeal trauma:
Injuries to larynx can be caused by penetrating wounds and blunt injuries.
Penetrating injuries: are caused by impact with sharp objects. Sharp objects always finds a path of least resistance. These objects slide off the laryngeal skeleton. The thyrohyoid membrane superiorly and the cricothyroid membrane inferiorly at risk in this type of injury.
Penetrating injuries involving the thyrohyoid membrane causes bleeding into paraglottic space. Rarely it could also lead to supraglottic stenosis. Voice is usually normal in these patients.
Penetrating injuries involving the cricothyroid membrane is associated with emphysema neck as air escapes into the soft tissues of neck. Bleeding into air way may cause airway obstruction.
Blunt trauma can be classified into :
Blunt trauma low velocity injury and Blunt trauma high velocity injury.
Features of Blunt trauma low velocity injury: Low velocity injuries cause bleeding into paraglottic space, swelling of tongue base, dysphagia, Reinke's space bleeding, and bleeding in to interarytenoid area causing air way compromise. Supra glottic stenosis can also occur in these patients. Rarely hyoid bone fracture can occur in these patients, but generally thyroid and cricoid cartilages are intact & undamaged.
Features of Blunt trauma high velocity injury: This type of injury is commonly associated with fractures of laryngeal skeleton. The degree if injury and pattern of injury is determined by the degree of calcification of thyroid cartilage. If the thyroid cartilage is uncalcified, its inherent elasticity helps it to spring back into its original position after the impact. Hence damage to uncalcified cartilages is minimal. Calcified thryoid cartilages has a tendency to fracture on impact. These fractures may be comminuted also.
This type of injury can also cause fixity of arytenoid cartilages.
The most dreaded injury is the one sustained by cricoid cartilage. This cartilage is the only complete ring in the whole of the respiratory system. Injury to this cartilage leads commonly to subglottic stenosis. In rare cases trachea may become separated from the cricoid cartilage resulting in death of the patient.
Pathological sequelae to laryngeal trauma:
Injury to hyoid bone: Fractures of hyoid bone heals without any complication. Rarely the fractured ends of hyoid may form a bursa resulting in malunion requiring surgical correction.
Thyroid cartilage: Fracture to thyroid cartilage causes chronic stenosis with resulting malfunction of larynx. Even minimal displacement of fractured fragments of thyroid cartilage is sufficient to cause changes in glottic resistance. Hence only non displaced fractures of thyroid cartilage should be managed conservatively while all displaced fractures will have to be surgically reduced and fixed. If perichondrium is stripped off the cartilage by blood clots, the cartilage becomes necrosed and dissolves. Mild mucosal denudation over the cartilages will cause inflammation of cartilage and formation of granulation.
Main treatment principles include:
1. Air way protection (very important)
2. Management of phonatory function of larynx.
Airway can be secured by performing a low tracheostomy (between the 3rd and 4th tracheal rings) in order to avoid further injuries to larynx and its supporting structures.
Before embarking on surgical intervention direct laryngoscopy and oesophagoscopy should be performed to access the degree of internal damage.
Indications for open surgical intervention:
1. Displaced / comminuted fractures of laryngeal skeleton: This is because fractures of laryngeal skeleton are intrinsically unstable secondary to muscular forces on larynx.
2. Vocal cord disruption / avulsion
3. Penetrating trauma to larynx
The larynx is approached via a skin crease incision at the level of cricothyroid membrane. Flaps are elevated subplatysmally superiorly up to the level of hyoid bone and inferiorly to the level of trachea. Strap muscles are retracted. Larynx is entered via a midline thyrotomy and the whole larynx is exposed. All mucosal lesions should be meticulously repaired taking care to ensure that no portion of cartilage is left exposed. Vocal cord injuries should be repaired using 5/0 or 6/0 absorbable vicryl. Avulsed vocal cords should be resuspended to the external perichondrium of thyroid cartilage.
Displaced cartilage fragments are reapproximated and fixed with wires / metal miniplates.
In extensive injuries after repair laryngeal stents can be used to fix the fractured fragements and to keep the airway patent. Generally stents should be considered if there is extensive endolaryngeal denudation of mucosa, disruption of anterior commissure tendon. These stents should be left in place atleast for a period of 2 weeks.
Stenosis is the most important complication of all laryngeal injuries.
Loss of voice.